In matrix acidizing, the aim is to create long conduits (wormholes) inside the reservoir formation which ultimately results in productivity increase. Acid in oil emulsion is used in the industry for stimulating carbonates with diesel commonly as the oil phase and hydrochloric acid (HCl) as the acid phase. Emulsifying HCl has numerous benefits over regular HCl. Perhaps the main benefit is deep penetration near the wellbore. Also, less corrosion damages are caused since the external phase is hydrocarbon (diesel). Several studies showed the success of replacing diesel as an external phase with other hydrocarbon oil, such as crude oil and xylene.

This work utilizes the extra hydrocarbon left unused –or sometimes dumped– from refineries, referred to as waste oil. The chemical composition of waste oil is studied. The HCl-waste-oil emulsion is prepared using 15 wt% HCl with a ratio of 70:30 of acid-to-oil. This paper reports results on the thermal stability and rheological properties of the HCl-waste-oil emulsion. All thermal stability experiments are conducted at a high temperature, 120 °C.

The results show that the HCl-waste-oil emulsion is a shear-thinning fluid. Power-law model is applicable seamlessly to all of the apparent viscosity data for all measured temperatures. The optimum conditions are found to be; 0.5vol% and 600 rpm for emulsifier concentration and mixing speed, respectively. Overall, the lab results show a promising potential for the HCl-waste-oil emulsion to be used in the field.

This work takes into account; reducing the budget of acidizing job along with environmental concerns. Apart from using low emulsifier concentration and low mixing speed, it makes use of the unwanted hydrocarbon from refineries.

Introduction

An emulsion is a combination of two immiscible liquids: oil and water. The emulsion is prepared using a mechanical and/or a chemical means to reduce the interfacial tension between the two immiscible liquids. Mechanical means such as providing enough agitation using a blender. Chemical means such as adding special surfactants. In both scenarios the interfacial tension is reduced resulting in an emulsion. Since the emulsion is thermodynamically unstable it is bound to separate into its parent liquids. Hence, stability of the emulsion is of critical importance for well stimulation applications. Obviously, combining the mechanical and chemical means will result in a more stable emulsion. In oil and gas industry, emulsions are widely used to stimulate wells in order to increase the productivity or injectivity. Emulsions are used with acid as the water phase and diesel as the oil one. For carbonate reservoirs, diluted HCl acid is the water phase; hence, referred to as emulsified acid.

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